Field of the Invention
The invention relates to a method for casting cast parts from a molten metal.
Description of Related Art
A fundamental problem when casting cast parts from a molten metal is to fill the mould with the molten material in such a way that as little air and oxide inclusions as possible occur in the cast part. In addition, with many applications, a certain course of solidification is sought, in order to obtain a microstructure formation which meets the respective requirements for the distribution of the mechanical properties.
It should also be added here that particularly when casting Al alloys the melt should get from the melt tank or casting vessel into the mould as quickly as possible. In this way, the case of alloying constituents reacting with the ambient oxygen and forming hard oxides is prevented. At the same time, the temperature losses during casting are to be minimised, in order to ensure an optimum microstructure formation. These requirements are faced with the risk that, when the melt is filled into the mould quickly, considerable turbulence occurs in the melt flow and gases are trapped in the cast part, whereby the formation of an optimum microstructure in the cast part is hampered.
Filling the respective casting mould with little turbulence “smoothly” is particularly important, especially where parts are cast which are required for constructing internal combustion engines, such as cylinder heads or crankcases, consisting of a light metal melt, in particular a melt based on aluminium. The amount of oxides and other impurities which swim on the melt volume to be filled into the casting mould and otherwise get into the casting mould during casting can hereby be minimised. In the past, a large number of variants of so-called “tilt casting” were developed in order to achieve this.
The common characteristic of the known tilt casting methods is that the casting mould is filled via a melt vessel coupled to it by rotating it with the melt vessel from a starting position, in which the melt vessel is filled with the melt to be cast, about a pivot axis into an end position, so that as a result of this pivoting movement the melt flows into the casting mould.
In one variant of tilt casting known from EP 1 155 763 A1, a casting mould with a pouring-in side pointing upwards is built onto a base plate and is then rotated with the base plate by approximately 180° about a horizontal pivot axis until the pouring-in side of the casting mould points downwards. Then, a casting vessel which is filled with a melt portion which is sufficient to fill the casting mould is coupled in a sealing manner with its pouring-out opening to the pouring-in side of the casting mould. The casting mould is subsequently rotated together with the casting vessel butting against it by approximately 180° about a horizontally aligned pivot axis, so that the melt flows out of the casting vessel into the casting mould. When the flowing-in process is complete, the casting vessel can be removed from the casting mould. Methods of this type are also called rotational casting methods due to the wide pivot distance covered.
A further method for tilt casting is known from DE 10 2004 015 649 B3, by means of which components consisting of light metal, in particular consisting of aluminium alloys, are cast. In this method, the melt is filled into a transverse run situated on the longitudinal side of a casting mould using head-casting. The casting mould is firstly tilted by an angle of 45° to 70° about its horizontally aligned longitudinal axis. Afterwards, filling the molten melt into the transverse run starts until about one fifth of the melt required for casting the component has been filled into the transverse run without the melt already flowing into the mould cavity of the casting mould. Then, the casting mould while melt is continuously filled further is rotated out of the tilted position into the vertical position such that the melt flows into the mould cavity along a casting mould wall.
A further variant of a method for casting components consisting of light metal according to the tilt casting principle is known from DE 10 2008 015 856 A1. In this method, the melt is filled into an assembly assigned to the casting mould. During a tilting movement of the casting mould, melt flows out of this assembly into the mould cavity. By pivoting the casting mould starting from an end position into a starting position of up to 90° about a horizontally aligned pivot axis by means of an assigned casting machine and by the casting mould then being displaceable in a range from 0° to 90°, geometrically exacting components with a good microstructure formation are supposed to be able to be cast within short cycle times in terms of solidification.
Finally, a method for tilt casting components is known from DE 10 2010 022 343 A1, in which in a first production step a casting mould, which defines a mould cavity for receiving a molten metal and has at least one pouring basin, is pivoted from a normal position with the pouring-in side pointing upwards in a first pivoting direction about a first pivot angle into a first pivot position. Then, the casting mould is prepared for casting a new cast part, in which it is cleaned, optionally coated and equipped with foundry cores. The casting mould is subsequently pivoted in a second pivoting direction which is opposite to the first pivoting direction. It thereby passes through the normal position and is pivoted as far as a second pivot position, in which the casting mould in relation to the normal position has a second pivot angle. Then, the at least one pouring basin is filled with a molten metal provided for casting a component. Subsequently, the one casting mould is pivoted together with the pouring basin in the opposite direction into the normal position in such a way that the molten melt between the second pivot position and the normal position flows into the mould cavity of the casting mould in a laminar manner. An advantage of this variant of tilt casting is supposed to be that the pouring basin is arranged relatively far away from the operator and so the thermal radiation affecting the operator is comparatively low. At the same time, this known method for tilt casting with shorter cycle times and hence higher output quantities is also supposed to enable components to be cast with a higher level of quality.
Against the background of the prior art explained above, an object of the invention was to provide a method for casting cast parts, in which with a further optimised mould filling procedure and an accompanying optimised course of solidification an optimum quality of the cast parts is ensured.